0 00:00:08,166 --> 00:00:09,686 - So let's begin the tale of the story 1 00:00:09,686 --> 00:00:11,005 of the George Washington Bridge 2 00:00:11,005 --> 00:00:12,796 from the social perspectives. 3 00:00:12,906 --> 00:00:14,586 So from the social perspective, 4 00:00:14,586 --> 00:00:16,486 Ammann needed the support of 5 00:00:16,486 --> 00:00:18,575 politicians and the community. 6 00:00:18,665 --> 00:00:20,286 He needed to sell his vision. 7 00:00:20,286 --> 00:00:22,386 And his vision had to be dramatic, 8 00:00:22,386 --> 00:00:25,406 it had to get the attention of the community 9 00:00:25,406 --> 00:00:27,426 and of the politicians, 10 00:00:27,426 --> 00:00:29,796 just the general public. 11 00:00:30,315 --> 00:00:33,546 By 1922, Ammann had formed a close 12 00:00:33,546 --> 00:00:35,206 but informal alliance with 13 00:00:35,206 --> 00:00:36,446 the governor of New Jersey, 14 00:00:36,446 --> 00:00:38,855 who at the time was George Silzer. 15 00:00:38,986 --> 00:00:40,946 And Silzer was very interested in improving 16 00:00:40,946 --> 00:00:43,886 the transportation, automobile transportation, 17 00:00:43,886 --> 00:00:45,066 in New Jersey. 18 00:00:45,066 --> 00:00:46,486 He felt that that would really 19 00:00:46,486 --> 00:00:49,106 help strengthen the economy of New Jersey. 20 00:00:49,106 --> 00:00:51,547 So he was very supportive of Ammann's idea 21 00:00:51,547 --> 00:00:55,086 of an automobile bridge in northern Manhattan 22 00:00:55,086 --> 00:00:57,796 where you see it exists today. 23 00:00:58,186 --> 00:01:00,246 In December of 1923, 24 00:01:00,246 --> 00:01:02,286 Ammann wrote a 22 page report, 25 00:01:02,286 --> 00:01:04,006 which he gave to Silzer, 26 00:01:04,006 --> 00:01:05,416 about the bridge. 27 00:01:05,416 --> 00:01:07,206 And this report wasn't just about the 28 00:01:07,206 --> 00:01:08,906 engineering aspects of the bridge, 29 00:01:08,906 --> 00:01:12,366 but it also included traffic, financing, 30 00:01:12,366 --> 00:01:15,616 and just the impact on the regional development. 31 00:01:16,006 --> 00:01:17,566 So he gave this report to Silzer 32 00:01:17,566 --> 00:01:19,526 who in turn gave the report to 33 00:01:19,526 --> 00:01:21,855 the Port Authority of New York. 34 00:01:22,726 --> 00:01:24,946 When Lindenthal found out about this report 35 00:01:24,946 --> 00:01:26,266 and what Ammann was doing, 36 00:01:26,266 --> 00:01:28,666 he was really upset, I guess, 37 00:01:28,666 --> 00:01:29,706 to put it mildly, 38 00:01:29,706 --> 00:01:33,046 and he called Ammann names like 39 00:01:33,046 --> 00:01:35,257 unethical and dishonorable. 40 00:01:35,425 --> 00:01:37,345 Of course, that wasn't Ammann's intention. 41 00:01:37,345 --> 00:01:39,865 Ammann tried to convince Lindenthal of that, 42 00:01:39,865 --> 00:01:42,286 but I can understand both points of view 43 00:01:42,286 --> 00:01:45,546 and how Lindenthal was seeing this 44 00:01:45,546 --> 00:01:46,836 from his side. 45 00:01:47,506 --> 00:01:49,006 So Ammann becomes, essentially, 46 00:01:49,006 --> 00:01:51,606 a politician for about three years, 47 00:01:51,606 --> 00:01:54,406 to move forward to sell people 48 00:01:54,406 --> 00:01:56,556 the idea of this bridge. 49 00:01:56,625 --> 00:01:59,547 And finally, on July 1st 1925, 50 00:01:59,547 --> 00:02:02,106 Ammann was hired by the Port Authority 51 00:02:02,106 --> 00:02:04,706 to design what we know now to be 52 00:02:04,706 --> 00:02:06,576 the George Washington Bridge. 53 00:02:07,206 --> 00:02:08,346 So when this bridge was built, 54 00:02:08,346 --> 00:02:11,826 we can imagine the transformation of communities, 55 00:02:11,826 --> 00:02:13,447 now we have New Jersey connected 56 00:02:13,447 --> 00:02:16,316 to New York City with automobiles, 57 00:02:16,366 --> 00:02:17,366 there's no longer that problem 58 00:02:17,366 --> 00:02:19,406 of the ferries being overworked 59 00:02:19,406 --> 00:02:22,367 and overcrowded with automobiles 60 00:02:22,367 --> 00:02:25,996 trying to cross the Hudson River on the ferries. 61 00:02:25,996 --> 00:02:26,946 Which is what Ammann was seeing, 62 00:02:26,946 --> 00:02:28,902 which was again what was inspiring him 63 00:02:28,902 --> 00:02:32,452 to say this needs to be an automobile bridge. 64 00:02:33,141 --> 00:02:34,699 And the next question, the next social question, 65 00:02:34,699 --> 00:02:38,278 because the social is tightly tied to the economy, 66 00:02:38,278 --> 00:02:41,039 is how was he able to double, essentially, 67 00:02:41,039 --> 00:02:42,640 the longest spanning bridge in the world, 68 00:02:42,640 --> 00:02:45,190 and still keep it economical? 69 00:02:45,539 --> 00:02:46,999 And to answer that question, 70 00:02:46,999 --> 00:02:48,919 I'm going to come to it when 71 00:02:48,919 --> 00:02:51,098 we talk about the scientific aspects 72 00:02:51,098 --> 00:02:53,009 of the George Washington Bridge. 73 00:02:53,359 --> 00:02:54,719 But first, let me talk a little bit 74 00:02:54,719 --> 00:02:56,129 about the symbolic aspects. 75 00:02:56,218 --> 00:02:57,699 So from the symbolic aspects 76 00:02:57,699 --> 00:03:00,379 we have both a symbol of the past 77 00:03:00,379 --> 00:03:02,359 and a symbol of the future 78 00:03:02,359 --> 00:03:04,419 in Ammann's vision and Ammann's 79 00:03:04,419 --> 00:03:05,649 design for this bridge. 80 00:03:06,059 --> 00:03:08,219 The symbol of the past were the heavy stone towers, 81 00:03:08,219 --> 00:03:11,069 which you don't see in the bridge today. 82 00:03:11,648 --> 00:03:14,139 But Ammann's design, his proposal was for 83 00:03:14,139 --> 00:03:15,869 heavy stone towers. 84 00:03:16,299 --> 00:03:18,239 So the steel skeleton that you see today 85 00:03:18,239 --> 00:03:21,319 the towers representing the George Washington Bridge 86 00:03:21,319 --> 00:03:23,719 that was the skeleton that was intended 87 00:03:23,719 --> 00:03:26,959 to support the stone facade, the granite facade, 88 00:03:26,959 --> 00:03:29,249 that was intended to go on those towers. 89 00:03:29,658 --> 00:03:31,619 But again, just like the Bayonne, 90 00:03:31,619 --> 00:03:32,839 this was during the Depression 91 00:03:32,839 --> 00:03:35,099 and to save money, that stone facade 92 00:03:35,099 --> 00:03:36,448 was left out. 93 00:03:36,800 --> 00:03:38,319 But Ammann's vision was very similar 94 00:03:38,319 --> 00:03:40,579 to what we know to be 95 00:03:40,579 --> 00:03:41,699 the Brooklyn Bridge. 96 00:03:41,699 --> 00:03:44,699 So we compare a sketch made by Cass Gilbert 97 00:03:44,699 --> 00:03:47,819 of the design of the George Washington Bridge, 98 00:03:47,819 --> 00:03:49,839 as was intended by Ammann, 99 00:03:49,839 --> 00:03:52,919 compare it to an image of the Brooklyn Bridge, 100 00:03:52,919 --> 00:03:54,538 you'll see some similarities, 101 00:03:54,538 --> 00:03:58,339 you see the stone arch abutments approaching the bridge, 102 00:03:58,339 --> 00:04:01,809 and you see the heavy stone towers. 103 00:04:02,099 --> 00:04:04,719 The difference is that for the George Washington Bridge 104 00:04:04,719 --> 00:04:06,819 the foundation is not on a caisson 105 00:04:06,819 --> 00:04:08,479 like in the Brooklyn Bridge. 106 00:04:08,479 --> 00:04:10,859 The Brooklyn Bridge towers needed to be heavy stone 107 00:04:10,859 --> 00:04:12,959 to sink those caissons, 108 00:04:12,959 --> 00:04:15,079 in this case, caissons were not used 109 00:04:15,079 --> 00:04:17,259 so the heavy stone towers 110 00:04:17,259 --> 00:04:18,569 were not needed. 111 00:04:18,819 --> 00:04:21,559 The symbol of the future is the very thin deck. 112 00:04:21,559 --> 00:04:24,359 So if you look at an image of 113 00:04:24,359 --> 00:04:26,099 the George Washington Bridge 114 00:04:26,099 --> 00:04:29,999 under construction and when it was finally completed, 115 00:04:29,999 --> 00:04:34,658 we see that the deck of this George Washington Bridge 116 00:04:34,658 --> 00:04:36,269 was very, very thin. 117 00:04:36,778 --> 00:04:40,339 At the time of completion, it only had one deck. 118 00:04:40,339 --> 00:04:43,479 So the top deck has eight lanes of traffic, 119 00:04:43,479 --> 00:04:45,699 today it has two decks, 120 00:04:45,699 --> 00:04:48,789 a lower deck has added six more lanes of traffic. 121 00:04:49,199 --> 00:04:51,379 So the original design was designed for 122 00:04:51,379 --> 00:04:53,399 two decks of traffic, 123 00:04:53,399 --> 00:04:54,999 but the second deck was intended 124 00:04:54,999 --> 00:04:56,918 to be put on there much later and 125 00:04:56,918 --> 00:04:58,819 it was put on there about 30 years after 126 00:04:58,819 --> 00:05:01,569 the completion in 1931. 127 00:05:02,199 --> 00:05:06,119 So this very thin deck was a symbol of the future. 128 00:05:06,119 --> 00:05:08,559 Symbol of future suspension bridges 129 00:05:08,559 --> 00:05:10,990 that were to be built in the 1930s. 130 00:05:11,519 --> 00:05:13,819 And it was this aesthetic that would 131 00:05:13,819 --> 00:05:16,219 lead some bridges into some trouble, 132 00:05:16,219 --> 00:05:18,528 as I'll talk about in a moment. 133 00:05:19,059 --> 00:05:21,479 So now let's look at the scientific aspects 134 00:05:21,479 --> 00:05:23,260 of this bridge, and the forces. 135 00:05:23,260 --> 00:05:25,139 In particular, let's look at the forces 136 00:05:25,139 --> 00:05:26,329 on the tower. 137 00:05:26,919 --> 00:05:29,899 So we have on the tower, the cables. 138 00:05:29,899 --> 00:05:31,459 And on top of that tower, 139 00:05:31,459 --> 00:05:33,279 we have the cables in the backspan 140 00:05:33,279 --> 00:05:35,119 that are pulling, the cables remember 141 00:05:35,119 --> 00:05:37,279 are in tension in this bridge. 142 00:05:37,689 --> 00:05:38,739 So there's this force, F, 143 00:05:38,739 --> 00:05:43,280 that's pulling down via the cable on the tower. 144 00:05:43,280 --> 00:05:45,559 And we can take that force F and 145 00:05:45,559 --> 00:05:49,399 split it into a horizontal and a vertical component. 146 00:05:49,399 --> 00:05:51,019 A horizontal component, H, 147 00:05:51,019 --> 00:05:52,989 and a vertical component, V. 148 00:05:53,519 --> 00:05:55,099 And if you would draw a box 149 00:05:55,099 --> 00:05:57,099 around those arrows, those arrows 150 00:05:57,099 --> 00:05:58,679 should be drawn so that 151 00:05:58,679 --> 00:06:01,430 they start and end at a corner of the box. 152 00:06:01,819 --> 00:06:04,199 And that will give you an indication of the magnitude 153 00:06:04,199 --> 00:06:05,179 of the force. 154 00:06:05,179 --> 00:06:06,579 So the lengths of those arrows 155 00:06:06,579 --> 00:06:10,099 are a relative indication of the size of each force, 156 00:06:10,099 --> 00:06:12,619 the relative size of the force F 157 00:06:12,619 --> 00:06:14,949 H, and V. 158 00:06:15,639 --> 00:06:18,460 The horizontal force H is equal to 159 00:06:18,460 --> 00:06:20,549 QL squared over eight D. 160 00:06:20,659 --> 00:06:23,039 Where Q is the load, it's a load 161 00:06:23,039 --> 00:06:25,459 in terms of force per length 162 00:06:25,459 --> 00:06:28,499 so kips per foot, for example. 163 00:06:29,419 --> 00:06:31,247 L is the span, remember the span 164 00:06:31,247 --> 00:06:34,256 is the distance between tower to tower. 165 00:06:34,256 --> 00:06:36,705 So it is the distance between two towers. 166 00:06:37,115 --> 00:06:39,495 And D is what we call the sag. 167 00:06:39,495 --> 00:06:41,055 So if you take that equation, 168 00:06:41,055 --> 00:06:43,475 H equals QL squared over eight D, 169 00:06:43,475 --> 00:06:47,515 we can say that QL over 8 represents the load, 170 00:06:47,515 --> 00:06:51,195 and L over D represents, essentially, 171 00:06:51,195 --> 00:06:52,885 the form of the bridge. 172 00:06:53,715 --> 00:06:56,255 So again, with L, the distance between the towers. 173 00:06:56,255 --> 00:06:59,235 D the sag, or the distance between 174 00:06:59,235 --> 00:07:02,735 the top of the tower and the bottom of that cable. 175 00:07:02,735 --> 00:07:04,815 We can play with those two dimensions 176 00:07:04,815 --> 00:07:07,105 and arrive at different forms for bridges. 177 00:07:07,935 --> 00:07:10,715 So if the bridge had shorter towers, 178 00:07:10,715 --> 00:07:13,915 or if the bridge had taller towers 179 00:07:13,915 --> 00:07:17,385 they would have a different value, D. 180 00:07:17,875 --> 00:07:19,775 So the question I have for you is, 181 00:07:19,775 --> 00:07:23,475 which design would result in the smallest force 182 00:07:23,475 --> 00:07:24,835 in the cable. 183 00:07:24,835 --> 00:07:26,615 Would it be the design 184 00:07:26,615 --> 00:07:28,435 with a shorter tower? 185 00:07:28,435 --> 00:07:30,395 Or a design with a taller tower? 186 00:07:30,395 --> 00:07:33,515 Or if you have no idea what I'm talking about 187 00:07:33,515 --> 00:07:36,395 you can answer, C, 188 00:07:36,395 --> 00:07:39,105 no idea, I'm still confused. 189 00:07:44,835 --> 00:07:46,635 The answer is that the taller tower 190 00:07:46,635 --> 00:07:49,135 has the smaller cable force. 191 00:07:49,135 --> 00:07:50,425 So let's see why. 192 00:07:51,155 --> 00:07:52,934 So if we look again, we draw that box. 193 00:07:52,934 --> 00:07:55,935 We know that the vertical force V, 194 00:07:55,935 --> 00:07:59,315 doesn't change depending on that distance 195 00:07:59,315 --> 00:08:00,665 that sag D. 196 00:08:00,756 --> 00:08:02,015 So V stays constant. 197 00:08:03,105 --> 00:08:05,075 But that force F will change. 198 00:08:05,075 --> 00:08:06,855 You can imagine that the angle of that 199 00:08:06,855 --> 00:08:09,116 force F is going to change if the tower 200 00:08:09,116 --> 00:08:11,355 is tall or the tower is short. 201 00:08:12,445 --> 00:08:15,995 So in which case, if you have that angle F 202 00:08:15,995 --> 00:08:18,475 change and it becomes longer H 203 00:08:18,475 --> 00:08:20,605 also becomes larger. 204 00:08:20,935 --> 00:08:22,476 Or you could just go back to the equation 205 00:08:22,476 --> 00:08:24,855 H equals QL squared over eight D 206 00:08:24,855 --> 00:08:28,325 and we know that if D is smaller, H is larger. 207 00:08:29,475 --> 00:08:31,455 So larger towers or taller towers 208 00:08:31,455 --> 00:08:33,416 means smaller cable forces, 209 00:08:33,416 --> 00:08:35,975 smaller cabler forces means smaller cables. 210 00:08:35,975 --> 00:08:39,795 So why not design the towers of suspension bridges 211 00:08:39,795 --> 00:08:41,325 as tall as possible. 212 00:08:41,755 --> 00:08:43,915 Because that would reduce material in the cable 213 00:08:43,915 --> 00:08:47,164 but the problem is that that adds material to the tower. 214 00:08:47,555 --> 00:08:49,415 So it's really a trade off between the cost 215 00:08:49,415 --> 00:08:52,395 of the tower and the costs of the cables. 216 00:08:53,715 --> 00:08:55,833 Continuing on the scientific aspect of the study 217 00:08:55,833 --> 00:08:57,233 let's answer that question of how 218 00:08:57,233 --> 00:09:00,653 Ammann was able to design the George Washington Bridge 219 00:09:00,653 --> 00:09:02,663 in a way to keep it economical. 220 00:09:03,533 --> 00:09:05,613 And the way he did it was looking 221 00:09:05,613 --> 00:09:06,774 at the traffic loads. 222 00:09:06,774 --> 00:09:08,573 How much traffic load will he design 223 00:09:08,573 --> 00:09:10,143 this bridge for? 224 00:09:10,412 --> 00:09:11,753 So he was designing essentially 225 00:09:11,753 --> 00:09:14,453 for a low probability of full truck loading. 226 00:09:14,453 --> 00:09:16,673 A low probability that every single lane 227 00:09:16,673 --> 00:09:19,743 would be back-to-back full of trucks. 228 00:09:20,333 --> 00:09:23,313 So at the time the equations 229 00:09:23,313 --> 00:09:25,833 or the methods that engineers used for 230 00:09:25,833 --> 00:09:27,793 designing bridges was such that 231 00:09:27,793 --> 00:09:30,753 traffic load, or the live load as it's called, 232 00:09:30,753 --> 00:09:34,173 these are the loads of the vehicles crossing the bridge 233 00:09:34,173 --> 00:09:37,813 is equal to the maximum conceivable load, 234 00:09:37,813 --> 00:09:41,593 so a bridge full, back-to-back of trucks, 235 00:09:42,953 --> 00:09:44,853 times one half, so about a half 236 00:09:44,853 --> 00:09:47,043 of a fully loaded bridge. 237 00:09:47,393 --> 00:09:49,743 That's what was designed at the time. 238 00:09:50,513 --> 00:09:53,953 Ammann used some equations using the length 239 00:09:53,953 --> 00:09:57,573 of the bridge, the span length and the number of lanes, 240 00:09:57,573 --> 00:10:01,013 using these variables he came up with a new proposal 241 00:10:01,013 --> 00:10:02,772 which essentially reduced the 242 00:10:02,772 --> 00:10:05,263 probability of full truck loading. 243 00:10:05,673 --> 00:10:07,713 So he proposed, instead of one half, 244 00:10:07,713 --> 00:10:10,493 a number for a bridge of this span, 245 00:10:10,493 --> 00:10:13,633 the number would be on the order of 1/6. 246 00:10:14,373 --> 00:10:16,474 So he reduced the load, or the live load, 247 00:10:16,474 --> 00:10:17,873 for something of this span, 248 00:10:17,873 --> 00:10:20,053 from something of the order of 249 00:10:20,053 --> 00:10:24,093 23 kips per foot or 23000 pounds per foot 250 00:10:24,093 --> 00:10:28,333 to on the order of 8000 pounds per foot. 251 00:10:28,333 --> 00:10:31,273 And this difference in how much load 252 00:10:31,273 --> 00:10:33,493 he was designing for was the difference 253 00:10:33,493 --> 00:10:35,473 of seven million dollars in savings 254 00:10:35,473 --> 00:10:37,843 for the George Washington Bridge. 255 00:10:38,873 --> 00:10:41,133 So the success of the George Washington Bridge 256 00:10:41,133 --> 00:10:43,933 led to a trend in bridge design 257 00:10:43,933 --> 00:10:46,565 that would become dangerous. 258 00:10:46,596 --> 00:10:48,315 This trend of thin decks, 259 00:10:48,315 --> 00:10:50,206 the symbol of the future. 260 00:10:50,755 --> 00:10:53,895 So next, let's look at this trend of bridge design, 261 00:10:53,895 --> 00:10:56,295 and what it meant for the bridges 262 00:10:56,295 --> 00:10:58,826 designed in the 1930s and on.